Some air compressor systems in use today utilize an adjustable relief valve that allows a user to select a desired air pressure that is to be applied to an air storage tank. When the valve is disposed in a full open position, the electric motor and air compressor are not loaded because the high pressure air supplied to the tank is vented to atmosphere via the relief valve. The motor includes an on/off switch that allows the primary and start windings of the motor to be connected to an external AC power source. A centrifugal mechanism typically is mounted on the motor shaft to allow the start winding of the electric motor to be disconnected from the external power source when the motor reaches full speed.
An unloader valve may be utilized to temporarily allow the air that is compressing under normal start-up or steady state off conditions to vent directly to the atmosphere instead of into the storage tank. This reduces the load initially applied to the motor and air compressor thereby allowing smaller, less expensive motors to be used. The unloader valve may not always be closed at the same point in time during operation because, for example, the pressure of the compressed air supplied from the air compressor varies with temperature.
Air compressor systems such as those described above typically are utilized in user attended applications where the motor and compressor are run for relatively short periods of time and the storage tank is compressed to a relatively low pressure. The user sets the adjustable valve to the desired pressure, turns the motor and compressor on and waits for the air storage tank to fill to the desired pressure. When the desired pressure is reached, the user shuts the motor and compressor off. Automatic operation wherein a pre-selected storage tank pressure level is maintained is uncommon in these applications.
Constructing an air compressor system that is to be utilized in a user attended application as discussed above is expensive and decreases the manufacturer's profit margin for each system that is sold. For example, material costs are unnecessarily high because a number of different single-use components are utilized and labor costs are unnecessarily high due to the time required for assembling the various components of the air compressor system.